We propose to study the effects of thyroid hormones on the ability of insulin, glucagon, and catecholamines to regulate glycogen phosphorylase and glycogen synthetase activities of hepatocyte isolated from rat. These studies will also examine the influence of hypothyroidism and hyperthyroidism cyclic AMP metabolism, adenylate cyclase activities, and hormone receptor status in order to probe the biochemical mechanism(s) associated with the ability of thyroid status to alter the hormonal regulation of hepatic carbohydrate metabolism.